Method for regulating a three-phase machine without a mechanical rotary transducer

ABSTRACT

A method is provided for regulating a three-phase machine functioning under any operational conditions without a mechanical rotary transducer. The machine is supplied with D.C. power by an inverter, where parameters of a D.C. link using an actual switching state of the inverter are detected for regulation. The method includes measuring (1) flow direction required for field-oriented control in asynchronous machines, and (2) rotor position for rotor-oriented control in synchronous machines. The measuring is performed by using spatial magnetic conductivity fluctuations in the machine. The conductivity fluctuations are detected using parameters for a D.C. link. An actual switching state of an inverter is used in the measuring process. Mathematical evaluation to calculate flow direction or rotor direction is then performed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a U.S. National Stage Application of International ApplicationNo. PCT/AT99/00025 filed Jan. 29, 1999 and claims priority under 35U.S.C. §119 of Austrian Patent Application No. A187/98, filed on Jan.30, 1998, the disclosure of which is expressly incorporated by referenceherein in its entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a method for regulating a three-phase machinewithout a mechanical rotary transducer, in particular an asynchronous orsynchronous machine, functioning under any operational conditions.

For high-precision regulation of three-phase machines, in particularasynchronous and synchronous machines, the latter either with permanentmagnet excitation, through reluctance effect, i.e. different magneticconductivity depending on the rotor position, or through a combinationof permanent magnet excitation and reluctance effect, the position ofthe magnetic flux is used. For machine speeds above a certain minimumflux rate, the induced electric current (EMC) can be detected by variousmethods described in the literature, and from it the flux position canbe determined. At low flux rates, the flux detection methods based onEMC fail. In this case methods can be used which detect the position orflux density-related magnetic conductivity in real-time, and determinethe rotor or flux indicator position from it.

In asynchronous machines, the main magnetic flux in the machine affectsthe magnetic leakage conductivity through saturation of the metal, sothat with real-time measurement of the magnetic leakage conductivity ora related coefficient the flux position can be determined. Insynchronous machines, the magnetic flux is directly correlated with therotor position, so that in synchronous machines the detection ofmagnetic flux or the detection of the rotor position can be used forfield-oriented regulation. In synchronous machines with permanent magnetexcitation without a significant reluctance effect, for example whenpermanent magnets are fixed to a cylindrical rotor, it is possible onsaturation in the iron—as with asynchronous machines thesaturation-related magnetic conductivity in relation to the fluxposition—to determine the flux position and also the rotor positionusing the leakage conductivity in machines with a damper or the mainfield factor in machines without a damper by means of real-timedetection or by detection of a related coefficient. In synchronousmachines with reluctance effect, the fluctuating magnetic conductivitydepending on the rotor geometry is detected instead of the fluctuatingmagnetic conductivity depending on the saturation, and thus the rotorposition is determined. In synchronous machines with permanent magnetexcitation and reluctance effect, the sum effect of the conductivityfluctuation depending on saturation and depending on geometry is used.

As described by M. Schrödl in the VDI Progress Reports, Series 21, No.117, VDI-Verlag, Düsseldorf 1992, “Sensorless Control of A.C. Machines”,by detection of the current space phasor and division by the voltagespace phasor a complex value that fluctuates with the double rotor orflux position can be obtained, which delivers the rotor position or theflux position via trigonometric equations. The disadvantage of themethod described there lies in the fact that for detection of thecurrent space phasor the detection of at least two phase currents usingexpensive phase current sensors, e.g. transfo-shunts, is necessary.

The aim of the invention is to create a method of the type mentionedabove, which on the one hand avoids the mentioned disadvantages, and onthe other hand guarantees a better and more precise control of themachine.

The method according to the invention is characterised by the fact thatin asynchronous machines the flow direction required for field- androtor-oriented control, and in synchronous machines the rotor positionare measured using the spatial magnetic conductivity fluctuations in themachine, whereby the conductivity fluctuations are detected using theparameters for the D.C. link, and in particular the D.C. link currentand/or D.C. link voltage, and using the actual switching state of theinverter, and by the fact that this is followed by a mathematicalevaluation. With this invention, it is for the first time possible tocreate a method for high-precision control of three-phase machineswithout a mechanical transducer, such as a position sensor ortachogenerator, which will work under any operating conditions,including low speeds and idle, whereby only parameters of the D.C. linksuch as D.C. link current or D.C. link voltage are measured. Thereby,using the actual inverter switching state, the ratio of phase currentincreases to the resulting voltages is determined, which correspondswith the flux or rotor position of the three-phase machine.

SUMMARY OF THE INVENTION

The basic idea is to detect the described conductivity fluctuations bymeasuring the current increases in the machine phases. The methodaccording to the invention avoids expensive current sensors, since itdoes not require the full space phasor information, but only theprojections of the current increase space phasor and the correspondingvoltage space phasor on the motor phase axes. The ratio of theseparameters (referred to as y with index of phase name) is proportionalto the actual local magnetic conductivity in the relevant phase axis,and fluctuates with the double rotor or flux axis position. Inaccordance with the invention, a measurement of the increase in D.C.link current using the actual inverter switching state is used fordetection of the phase current increases instead of a measurement of thephase current increases. Thereby, the inverter serves as an intelligentmeasuring point change-over switch that applies the different motorphases to the D.C. link current measuring module depending on theinverter state. Thereby, the operational inverter states—the machinecontrol is not affected by the measurement—or forced inverter states—themachine control is affected by the measurement—can be used. If, forexample, positive D.C. link voltage is applied to the inverter branchconnected to phase U in a three-phase inverter, and negative D.C. linkvoltage is applied to the inverter branches connected to V and W, thephase current of phase U will necessarily flow in the D.C. link, andtherefore this phase current will be detected via the D.C. link. At thesame time, however, it is known that in this inverter combination thevoltage space phasor applied to the machine points in the direction ofphase U, so that the mentioned ratio of the projections of the currentincrease space phasor—in the mentioned case, this is the currentincrease in phase U—and the corresponding voltage space phasor—in thiscase the voltage space phasor in phase direction U—can be established onthe motor phase axes. Therefore, yu is established. By means of athree-phase inverter and a three-phase machine, the mentioned ratios cantherefore be established via six inverter states in the directions U,−U, V, −V, W, −W.

In accordance with a special feature of the invention, at least twomeasurements of the increase in D.C. link current are carried out, andthe measured values of the two increases are entered into the statorvoltage equations and linked mathematically. An important advantage ofthis method according to the invention is the fact that the samemeasuring module is always used, so that errors of measurement due tocomponent leakage, etc., are compensated by the combination of severalmeasurements and thus do not affect the result. With this embodiment ofthe invention with the combination of two measurements, the EMC can beeliminated and the conductivity measurement is therefore independent ofspeed. This is not possible in measurement of the current space phasorfor at least two phase currents, since the involved current sensors havedifferent errors of measurement that affect the result.

In accordance with a further embodiment of the invention, at least twoconductivity measurements are carried out in spatially separatedirections, and the angle γ is calculated according to the known rulesof calculation. If an induced voltage (EMC) occurs in the stator windingdue to a turning rotor, the ratio y will be affected by the EMC. Inorder to eliminate this influence, two current increase measurements arecombined and instead of the voltages the differences in voltage andinstead of the current increases the differences in current increasesbetween the two measurements that are to be combined are used. This isshown by writing down the stator voltage equations for the twomeasurements to be combined, and subtraction of the two equations. Sincethe EMC appears additively on the right-hand side of the equation, it iseliminated by the subtraction. The mathematical evidence can be found inVDI Progress Reports, Series 21, No. 117, VDI-Verlag, Düsseldorf 1992,“Sensorless Control of A.C. Machines” by M. Schrödl. As a result, thedetection of conductivity fluctuations is independent of speed. Sincethe actual rotor or flux position angle cannot be concluded accuratelyfrom one conductivity measurement, at least two conductivitymeasurements in spatially different directions are combined. Thus, whenlinear, independent conductivity measurements A, B, C are available withthe corresponding model equations for the conductivity fluctuations

 yA=ymean+Δy cos(2γA−2γ)

yB=ymean+Δy cos(2γB−2γ)

yC=ymean+Δy cos(2γC−2γ)

which correspond with the double differential angle between the voltagedifference space phasor γA etc., and the direction of the conductivitymaximum γ, which corresponds with the rotor position or flux directionaccording to the above descriptions, depending on the type of machine,the parameter ymean (mean conductivity) and Δy (conductivityfluctuation) can be eliminated and the angle γ calculated using knownrules of calculation.

In accordance with another special feature of the invention, theconductivity values detected by means of measurement are detected atdifferent D.C. link voltages with sufficient accuracy. A D.C. linkvoltage detection is not necessary, if the combined conductivitymeasurements were carried out at more or less the same D.C. linkvoltage, since the parameter for voltage in the above equations thenpresents a constant factor that is the same in every equation and istherefore eliminated when calculating the angle γ. The angle γ is thebasis of the known field- or rotor-oriented control for the independentsetting of flux and torque in three-phase machines, whereby this controlis also possible at low speeds and standstill when using the methodaccording to the invention for rotor or flux position without a rotorposition sensor or tachogenerator.

According to a further feature of the invention, speed- and/orload-dependent correction functions, preferably linear, in the form:

γ(corrected)=γ+Δγ(speed, load)

are carried out in the mathematical calculation. Speed- andload-dependent influences on the conductivity curve can be taken intoaccount by means of speed- and load-dependent, preferably linearcorrection functions in the above forms in order to improve accuracy,whereby the correction functions using a reference model, for example aflux model according to the state of the art in asynchronous machines,or a reference transducer, for example rotation angle measurement insynchronous machines, are determined once per type of machine.

In accordance with a further feature of the invention, the determinedflux or rotor position angle is used as an input parameter in a machinemodel for on-line control of the three-phase machine. Thus, theapplication of this method according to the invention is clearlyguaranteed in terms of function.

According to an aspect of the present invention, a method for regulatinga three-phase machine functioning under any operational conditionswithout a mechanical rotary transducer, which is supplied with D.C.power by an inverter, and where parameters of a D.C. link using anactual switching state of the inverter are detected for regulation isprovided. The method comprises measuring one of (1) flow directionrequired for field-oriented control in asynchronous machines, and (2)rotor position for rotor-oriented control in synchronous machines, byusing spatial magnetic conductivity fluctuations in the machine, wherebythe conductivity fluctuations are detected using parameters for a D.C.link. Also included in the method is the use of using an actualswitching state of an inverter. Mathematical evaluation to calculate oneof flow direction or rotor direction is then performed.

According to another aspect of the present invention, the machine is oneof an asynchronous and synchronous machine. In another aspect of theinvention, the method further includes detecting the conductivityfluctuations using parameters for at least one of D.C. link current andD.C. link voltage. In another aspect of the present invention, themethod includes carrying out at least two measurements of an increase inD.C. link current; and entering the at least two values from themeasurements into stator voltage equations and linking the measurementsmathematically.

In another aspect of the present invention, the at least twoconductivity measurements are carried out in spatially separatedirections, and the values are introduced into the following equations:

yA=ymean+Δγ cos(2γA−2γ)

yB=ymean+Δγ cos(2γB−2γ)

yC=ymean+Δγ cos(2γC−2γ)

wherein the angle γ is calculated.

According to a further aspect of the present invention, the methodincludes conductivity values detected by measurement are detected atdifferent D.C. link voltages with sufficient accuracy. In another aspectof the present invention, at least one of speed-dependent andload-dependent correction functions are carried out in a linearmathematical calculation defined by γ(corrected)=γ+Δγ(speed, load).According to still a further aspect of the present invention, the methodincludes using one of a determined flux or rotor position angle as aninput parameter in a machine model for on-line control of a three-phasemachine.

In another aspect of the invention, a method for regulating athree-phase machine functioning under any operational conditions withouta mechanical rotary transducer, which is supplied with D.C. power by aninverter, and where parameters of a D.C. link using an actual switchingstate of the inverter are detected for regulation is provided. Themethod includes, measuring at least one of (1) flow direction requiredfor field-oriented control in asynchronous machines, and (2) the rotorposition for rotor-oriented control in synchronous machines, by usingspatial magnetic conductivity fluctuations in the machine. Theconductivity fluctuations are detected using parameters for a D.C. link;using an actual switching state of an inverter; and performing amathematical evaluation to calculate the flow direction or rotordirection, wherein the at least two conductivity measurements arecarried out in spatially separate directions, and the values introducedinto the following equations:

yA=ymean+Δγ cos(2γA−2γ)

yB=ymean+Δγ cos(2γB−2γ)

yC=ymean+Δγ cos(2γC−2γ)

wherein the angle γ is calculated.

BRIEF DESCRIPTION OF THE PRESENT INVENTION

The invention is explained in more detail on the basis of the embodimentillustrated in the FIGURE.

The FIGURE shows the control of a three-phase machine in a schematicdiagram.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In accordance with the FIGURE, an inverter 1 is supplied by a one- orthree-phase A.C. power system at the optional A.C. input 2. The D.C.side 3 is connected to the converter 4, which has the semiconductorvalves 5, by the D.C. link zk. The D.C. link voltage Uzk of themeasuring and control unit 7 is fed by a capacitor 6. Moreover, the D.C.link current Izk of the measuring and control unit 7 is also fed by theresistor R. The actual switching state of the inverter I is alsodetected by the measuring and control unit 7. The three-phase machine 8to be regulated is connected on the bridge circuit of the semiconductorvalves 5. The converter 4 is controlled by means of the control signals9 calculated by the measuring and control unit 7.

In conclusion, it is noted that in the various described embodiments thesame parts are allocated the same reference numbers and the samecomponent names, whereby the disclosures contained throughout thedescription can be applied by analogy to the same parts with the samereference numbers or same component names. Furthermore, positionsdetails given in the description, e.g. top, bottom, side, etc., relateto the figure being described and illustrated at the time and with achange of position should be transferred accordingly to the newposition. Moreover, individual features or combinations of features fromthe different embodiments illustrated and described can representindependent inventive solutions or solutions according to the inventionin themselves.

The problem forming the basis of the separate solutions according to theinvention can be taken from the description.

For form's sake, it is noted that for a better understanding of thestructure of the control, the components are illustrated partly untrueto scale and/or are enlarged and/or made smaller.

What is claimed is:
 1. A method for regulating, without a mechanicalrotary transducer, a three-phase machine, which, functioning under anyoperational conditions, is supplied with D.C. power by an inverterthrough a D.C. link, the method comprising: detecting parameters of theD.C. link related to spatial magnetic conductivity fluctuations of themachine; monitoring an actual switching state of the inverter; andcalculating at least one of (1) flux direction required forfield-oriented control in asynchronous machines, and (2) the rotorposition for rotor-oriented control in synchronous machines from thedetected parameters of the D.C. link and the actual switching state ofthe inverter, wherein at least one of speed-dependent and load-dependentcorrection functions are carried out in a mathematical calculationdefined by γ(corrected)=γ+Δγ(speed, load).
 2. The method of claim 1,wherein said machine is one of a synchronous and an asynchronousmachine.
 3. The method of claim 1, whereby the conductivity fluctuationsare detected using parameters for at least one of D.C. link current andD.C. link voltage.
 4. The method of claim 1, further comprising carryingout at least two measurements of an increase in D.C. link current; andentering the at least two values from the measurements into statorvoltage equations and linking the measurements mathematically.
 5. Themethod of claim 1, wherein conductivity values detected by measurementare detected at different D.C. link voltages with sufficient accuracy.6. The method according to claim 1, further comprising using one of adetermined flux or rotor position angle as an input parameter in amachine model for on-line control of a three-phase machine.
 7. A methodfor regulating, without a mechanical rotary transducer, a three-phasemachine, which, functioning under any operational conditions, issupplied with D.C. power by an inverter through a D.C. link, the methodcomprising: detecting parameters of the D.C. link related to spatialmagnetic conductivity fluctuations of the machine; monitoring an actualswitching state of the inverter; and calculating at least one of (1)flux direction required for field-oriented control in asynchronousmachines, and (2) the rotor position for rotor-oriented control insynchronous machines from the detected parameters of the D.C. link andthe actual switching state of the inverter, wherein the at least twoconductivity measurements are carried out in spatially separatedirections, and the values introduced into the following equations:yA=ymean+Δy cos(2γA−2γ) yB=ymean+Δy cos(2γB−2γ) yC=ymean+Δy cos(2γC−2γ)wherein the angle γ is calculated.
 8. The method of claim 7, wherein atleast one of speed-dependent and load-dependent correction functions arecarried out in a linear mathematical calculation defined byγ(corrected)=γ+Δγ(speed, load).
 9. A method for regulating, without amechanical rotary transducer, a three-phase machine, which, functioningunder any operational conditions, is supplied with D.C. power by aninverter through a D.C. link, comprising: measuring at least one of (1)flux direction required for field-oriented control in asynchronousmachines, and (2) the rotor position for rotor-oriented control insynchronous machines by using spatial magnetic conductivity fluctuationsin the machine, whereby the conductivity fluctuations are detected usingparameters for the D.C. link; monitoring an actual switching state ofthe inverter; and performing a mathematical evaluation to calculate theflux direction or rotor direction, wherein the at least two conductivitymeasurements are carried out in spatially separate directions, and thevalues are introduced into the following equations: yA=ymean+Δycos(2γA−2γ) yB=ymean+Δy cos(2γB−2γ) yC=ymean+Δy cos(2γC−2γ) wherein theangle γ is calculated.